Controlling the granulometry of material

ABSTRACT

Apparatus for and method of automatically providing a constant granulometry of comminuted materials, by making simultaneous measurements of variables with respect to a given mesh to form an output signal, comparing said signal with a reference signal obtained from one of a family of characteristic grinding curves and generating from the resulting signal the corrections necessary to maintain the granulometry constant.

D United States Patent l 13,568,938

[72] Inventors Paul Marcel Emile Barrot [56] References Cited Clichy; UNFTED STATES PATENTS Luck 3,092,337 6/1963 Patterson 241/34 3223s; 12/122; 2211143; [22] Filed May171968 3 480 212 11/1969 L' l i i 241/34 [45] Patented Mang 1971 l egrene a [73] Assignee Societe Anonyme: Babbitless P ima y Examiner-Frank T. Yost Paris, France Attorney-Baldwin, Wight & Brown [32] Priority May 31, 1967 [33] France 108,609

[54] CONTROLLING THE GRANULOMETRY OF ABSTRACT: Apparatus for and method of automatically MATERIAL providing a constant granulometry of comminuted materials,

40 Chums 9 Drawmg by making simultaneous measurements of variables with [52] US. Cl 241/24, respect to a given mesh to form an output signal, comparing 241/34, 241/37 said signal with a reference signal obtained from one of a fami- [51] Int. Cl. B02c 4/32 1y ofrcharaeteristic grinding curves and generating from the [50] Field of Search 241/24, 34, resulting signal the corrections necessary to maintain the granulometry constant.

PATENTED HAR 9 l97| SHEET 2 0F 9 PATENTEU MAR 9 I9?! SHEET 3 BF 9 PATENTED MAR 9197:

SHEET 4 (IF 9 raL XXX

PATENTED MAR 9197: 3,568,938

sum 5 0F 9 PATENTE U MAR 9 I97! SHEET 8 OF 9 PATENTED MAR 919m sum 7 or 9 SHEET 9 UF 9 NOVA,

PATENTED m 9191:

t couraottruo run GRANULOMETRY or MATERIAL The present invention relates to a method for the automatic regulation of the particle size distribution of granules produced by grinders and crushers, particularly gyratory grin ders and crushers, in such a manner as to maintain the particle size distribution permanently at a desired value irrespective of the physical state of the materials treated and the wear of the grinding parts. The invention likewise relates, to the devices serving to carry out this method, and also to grinders and crushers, particularly gyratory grinders and crushers, which are equipped therewith.

The particle size distribution, in this Specification hereinafter referred to as the granulometry, of crushed or ground mineral products is of capital importance for an increasing number of industrial applications, and the ability to regulate granulometry at will in a reliable manner is becoming an essential need. The situation is for example as follows:

1. For roadmaking materials, the specifications of most Traffic Authorities lay down grading curve envelopes within which the grading curve of the materials to be used must be kept. Any variation in grading which results in a curve falling outside the envelopes in question entails penalties and may result in the complete refusal of the goods.

2. For the manufacture of concrete, the grades in demand are always closely tied to the granulometry of the aggregates. The cost price of concretes also depends to a large extent'on this granulometry.

3. For ores, the granulometry has a considerable influence on the cost of the treatments to which the ores are subjected and also on the quality (and therefore the value and cost price) of the metals obtained.

4. For coals, market value is closely tied to granulometry.

5. For all other minerals, granulometry is a factor, and frequently the essential factor, in their efficient utilization.

lt is therefore clear that it would be a major advantage to be able on the one hand to verify continuously the granulometry of a material leaving a grinding or crushing process, and on the other hand to regulate and correct the granulometry automatically during the operation, taking into account both variations in the material and the wear of the grinding parts, so as to make the granulometry conform to the desired value.

Various means have already been proposed in the attempt to maintain the production of a grinder or crusher at its optimum value, utilizing for example the input power/output ratio, considered as constant. Actually, this ratio cannot be considered as constant, because it does not take into account either variations in the resistance to compression of the materials, which are not always identical at all points in the same quarry, or the granulometry of the materials introduced, which is dependent on the fragmentation effected by cutting in the quarry or on the variable conditions of utilization of the grinder or crusher. ln addition this ratio does not take into account the granulometry of the crushed materials, which is dependent on numerous parameters, such as the hygrometric condition of the materials, state of cleanliness, etc. These circumstances have the effect that equal outputs do not therefore automatically correspond to an equal input power. The ratio taken into account in this method of regulation does not therefore ensure that the products leaving the apparatus will have the required granulometry and consequently, automatic regulation based on this method is very haphazard.

Because of these rather disappointing results, the advantage referred to above of actually being able to obtain a given granulometry which is substantially constant from grinding or crushing operations has led to a continuation of research with a view to obtaining satisfactory results. For this purpose it may be appropriate to review in detail all the information gained from previous work and experiments.

it is known that products leaving a crusher or grinder have a granulometry which is dependent on:

a. the type and characteristics of the crusher, grinder, or other similar apparatus used;

b. the nature, physical state, and granulometry of the minerals to be crushed; and

c. the fineness to which these products are crushed or ground, this finenessbeing characterized by the dimension of the largest element contained in the products leaving the crusher, grinder, or other apparatus.

Practically all crushing, grinding, or other similar appliances are provided with one or more means of regulation the object of which is to vary the fineness of the products obtained. Thus in:

a. crushers or grinders of the gyratory" type a device is provided for regulating the relative positions of the inner and outer crushing cones;

b. in crushers or grinders of the jaw" type, a device is provided for adjusting the relative position of the fixed and movable jaws;

c. in ball or bar grinders or pulverizers, a device is provided for regulating the feed;

d. in cylinder grinders a device is provided for adjusting the spacing of the cylinders.

Grinding and crushinghave been studied experimentally for a long time for the purpose of determining the relation existing between the fineness of theproducts obtained and the granulometry of said products. The method has been adopted of defining generally the granulometry of a previously ground or crushed mineral product by a curve obtained by plotting as abscissae the dimension of the mesh of the test sieve and as ordinates the percentage of particles passing through this mesh, or vice versa.

Similarly, the fineness of a product leaving a crusher, grinder, or similar apparatus is genenally defined by a single point on this granulometric curve, this point being situated near the apex of the curve corresponding to the largest particles contained in these products. Thus, for example, it is commonly said that a product has a fineness of 10 percent material retained on a screen of 20mm square mesh, or else that the crusher was adjusted to give at the outlet a fineness of i0 percent material retained on the screen of 20 mm square mesh; verification of this fineness is then effected by manual or mechanical screening.

in this connection, numerous tests have been carried out over a very long period of time, both by manufacturers and by users, with a view to determining the granulometric curves which for the same mineral and the same type of crusher or grinder correspond to the different finenesses which this crusher or grinder make it possible to obtain.

These characteristic curves of a given crushed or ground mineral in an apparatus of a determined type, for the different finenesses which can be obtained with the fineness adjusting devices of the crusher or grinder, are obtained in the form of a family of affine characteristic curves, that is to say curves which are deduced from one another by a simple change of ordinates, in a determined ratio. This property appears clearly in the family of characteristic granulometric curves shown in FIG. 1, these curves being obtained from hard, tough materials with the aid of BABBITLESS" secondary gyratory crushers made by the applicants assignee. In these curves the mesh dimension of the test sieves is shown as abscissae and the percentage of particles passing through the mesh is shown as ordinates.

Examination of these curves shows that for a given mineral or class of minerals, once the family of characteristic curves defining the granulometry at the outlet of the crusher or grinder of a given type is available, it is sufficient to determine a single point on the granulometric curve of the product obtained, or for example to give the fineness of said product, to be able to plot this granulometric curve completely by simple reference to the other curves of the family.

These doctrines, which are currently applied in practical grinding and crushing, have the result that:

on the one hand, verification of the granulometry of the product may be replaced by verification of the fineness of the product, which is a considerably simpler check because it relates to a single point on the granulometric curve; and

on the other hand, when it is desired to obtain a crushed or ground product having a particular granulometric curve lying within a family of characteristic granulometric curves, it is sufficient to adjust the crusher or grinder to give products having a fineness corresponding to one point on the desired granulometric curve.

The idea has now been put forward of utilizing the ratio percentage remaining on a given mesh which represents percentage of material passing through, the fineness for the given mesh, for the automatic and continuous determination, at any desired frequency of measurement, of the fineness of products after treatment and also for the maintenance, within a clearly defined zone, of the granulometry corresponding to this fineness. in addition, it has been proposed to utilize for this purpose the capability of determination of a granulometric curve from a single point on the curve, for a given apparatus. Put another way, as one of the objects of the invention it has been proposed to utilize these properties for the automatic correction, during operation, of the adjustment of an apparatus so as to neutralize the effect of the variations of the different above-mentioned parameters which are capable of affecting the fineness of the products, so as to restore and maintain the operating conditions of the apparatus which correspond to a predetermined granulometric curve.

In its most general definition therefore the invention consists in compensating continuously or periodically, from a point of a curve obtained in the course of operation, any variations of fineness and hence of granulometry which may occur during the operation of an apparatus for any reason whatsoever, such as for example the wear of the grinding parts or variations in the nature, physical state, or granulometry of the products feeding the apparatus. The invention thus has the object of regulating and automatically maintaining a constant granulometry from a single point of a curve selected in accordance with requirements, and makes it possible to follow a programme defined in advance for a given working period, whatever the evolution of parameters capable of varying the granulometry, whether these relate to the feed or to wear of the grinding parts of the apparatus.

A method of controlling the output granulometry of a material from a crusher or grinder,.for which a characteristic family of curves has been established defining the granulometry of the material for different settings of the grinder or crusher, comprises;

a. making simultaneous measurements of any two of the following variables with respect to a given mesh,

1. total rate of fiow of material to the mesh,

2. rate of flow of material passing the mesh,

3. rate of flow of material retained on the mesh, or of the rate of flow of material passing the mesh and the rate of flow of material passing the mesh at a point spaced from the pint of the first measurement in the direction of flow, said simultaneous measurements being made at predetermined frequencies,

b. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves, and

c. causing said output signal to generate the control forces adjusting the setting of the grinding faces of said grinder or crusher or of a feeding device to the grinder or crusher so as to restore the output signal to the desired value.

The quantities representing the material retained on a given mesh and the material passing through may be taken from the main circuit or from a sampling circuit; they may be either the quantity of material retained and the quantity of material passing through the given mesh or the quantity of material retained on the given mesh and the total production, or finally they may be the amount of material passing through and the total production.

For the purpose of carrying out the method all or part of the materials crushed to a determined mesh may advantageously be screened with the aid of a vibrating screen or other suitable apparatus, the quantities representing material retained and material passing through for the determined mesh being measured, and these measurements being transmitted to an electric, electronic, or other calculating device to determine the ratio between the said quantities. The result given by the calculator serves to operate any suitable known means for the purpose of modifying the relative position of the grinding parts if this result, that is to say this ratio, is not within a predetermined range.

If for example the wear of the grinding parts results in an increase of the quantity of material retained in relation to the quantity of material passing through, the ratio of these two values will no longer be within the detennined range and the automatic means will modify the relative position of the grinding parts so as to reduce the amount of material retained and thus bring the ratio back inside the range. Similarly, if this ratio is reduced, for example as the result of a change in the granulometry of the materials introduced into the crusher, the automatic means will cause an alteration in the relative position of the grinding parts in the opposite direction.

The method according to the invention may be applied to all types of grinders and crushers, and particularly to suspension type or remotely controlled hydraulically adjustable gyratory crushers.

Known apparatuses contain a safety device which, by automatically moving the grinding parts away from one another as soon as an abnormal force occurs, makes it possible to remove foreign bodies which may be contained in the materials to be ground so as to prevent clogging between the grinding parts. The presence of this device is not compatible with the granulometric stability which is desired and is obtained according to the present invention unless, after elimination of the overload, it automatically returns the grinding parts to the exact relative position which they occupied before the intervention of the safety device.'

For this reason apparatus for carrying out the method according to the invention comprises a detector for sensing the displacement of one of the grinding parts, a contactor connected to said detector and containing at least one pancake coil having a number of contact studs, some of which transmit the various positions of the grinding part to a recorder or to a display panel, while the others transmit the information of a grinding programme, taking into account the positions indicated, to the control means of the grinder or crusher.

In a gyratory crusher it is the position of the inner grinding cone which varies in relation to that of the outer grinding cone, the shaft carrying the inner grinding cone performing a pendular movement and also a movement of rotation about itself which is due to the forces applied by the grinding of the materials on the inner cone. in the case of a gyratory crusher of this type the position detecting device is arranged so as to transmit the axial displacement of the shaft into a rectilinear movement, despite the existence of the pendular movement of said shaft.

For a gyratory crusher of this type the position detecting device according to the invention comprises a collar surrounding and secured to the shaft so as to allow relative rotary movement of the shaft with respect thereto but so as to prevent relative axial movement therebetween, a feeler rod which is integral with the collar at one end and the other end of which carries a part of circular section, such as a cylinder or a sphere, a detector, such as a fork, disposed at the level of said part so as to follow only the axial displacement of the shaft and to allow said part to make all eccentric movements, a second feeler rod rigidly connected to the detector and parallel to the axis of the crusher in such a manner as to be able to slide freely in a cylinder fixed on the frame of the crusher, said second feeler rod being connected to control, and recording means in electrical contact with hydraulic means adapted to cause axial displacement of the shaft.

The movement detector collar is preferably held fixed in respect of rotation by means of flexible parts capable of absorbing the eccentric movement due to the pendular movement of the shaft whilst still enabling the shaft to rotate in the bore in said collar. The collar therefore follows the rising and falling movements of the shaft dictated by the adjustment.

The part of circular section is, for example, a roller or a ball which, because of the mechanical connection, follows the movementdescribed by the shaft during the operation of the apparatus. This part consequently performs an eccentric movement corresponding to the pendular movement of the shaft.

The assembly comprising the collar, the feeler, and the part of circular section may be replaced by a body of revolution coaxial to the shaft and mounted on and rotating with the latter.

The detector is preferably a U-shaped fork which encloses the roller or ball or the outer edge of the body of revolution, namely a cylinder or sphere, in order to neutralize the pendular movement and to undergo only the axial displacement of the shaft. The distance between the two arms of the U-shaped fork is made sufficiently great to enable the eccentric movement of the part to take place freely and to ensure that the fork will follow only the axial movement of the shaft. If the shaft performs a rising or falling movement it drives the detector or fork by means of the assembly comprising the collar, feeler, ball or roller or the body of revolution. In order to prevent this detector from being subjected, at any particular position, to the shocks of the movement of the cylinder or of the part connected to the collar of the shaft during the eccentric movement of normal operation, it is necessary to hold the detector fixed so that the movement described by said part will be inscribed in said detector without touching its sides.

For this purpose, the rod of the detector is prevented from moving under its own weight by means of for example a compression spring, stuffing-box, seal, or braking plate bearing against the rod carrying the detector, by magnetic braking (permanent magnet or electromagnet) or by any other known braking device. The rising and falling movement of the shaft, which always performs a pendular movement and a rotation about itself, is thus converted by this detector into a linear movement from which it is possible to retransmit all the positions of the shaft to a central control station.

The method according to the invention also permits the automatic regulation of p a group comprising a plurality of crushers, grinders, or similar apparatuses, constituting for example a complete crushing installation, so that the final granulometry of the products leaving the installation will be in conformity with a predetermined granulometry.

it is therefore clear that the process according to the invention, which enables each crusher, grinder, or other similar apparatus to be regulated individually and automatically so as to obtain at its outlet products having a predetermined granulometry, also makes it possible (for example with the aid of punched cards) to establish and carry out automatically a general programme relating to the final granulometry of the entire production of a factory, the operation of which then becomes entirely automatic.

Several embodiments of the method according to the invention are described below with reference to FIGS. 2-8 of the accompanying drawings in which:

FIG. 1, previously referred to, is a family of characteristic granulometric curves obtained from hard, tough materials;

FlG. 2 is a diagrammatic view of a gyratory crusher to which control of the total production of the crusher is applied;

F lG. 3 is a diagrammatic view of a gyratory crusher in which the control is effected by samples taken from the production of the crusher;

FIG. 4 is a diagrammatic view of a variant of the control system shown in FIG. 3;

FIG. 5 shows a view in section of an automatic control device for the movable crushing part;

FIG. 6 is a view in section seen from arrow F along the line VI-Vi in FIG. 5;

FIG. 7, 7a, 7b, 7c is a developed wiring diagram of the control system of the device regulating the position of the movable grinding part with the aid of the indications; and

FIG. 8 is a view of a manual device controlling the grinding position.

In the drawings the method of the invention is shown applied to a hydraulic suspension type gyratory crusher in which the position of the inner grinding cone mounted on the pendular shaft, in relation to the outer grinding cone fixed in the frame of the apparatus, is adjusted by remote control by varying the volume of oil contained inside the suspension actuator of the shaft.

FIGS. 2 and 3 show the gyratory crusher 1 with its outer crushing cone 1a and its inner crushing cone 1b. The installation contains a discharge conveyor 2, a screening device 3 including meshes 3a, 3b and the determining mesh 3c a conveyor 4' carrying the material retained at mesh 3c to a first weighing apparatus, and a conveyor tSreceiving the material passing through the mesh 30 and carrying it to the outlet after weighing in a weighing apparatus 7 of any known type.

The output signals from the two weighing apparatuses 5 and 7 are connected to an electronic calculator 8 which calculates the ratio of the weights measured by the two apparatuses. The output 8' of the calculator 8 represents the value of the ratio and is transmitted to the control of any known type of hydraulic device 9 which effects the displacement, when required, of the suspension actuator It by means of fluid pumped through the pipe 9. The transmission of the output signal of the calculator 8 is interrupted when the value of the ratio material retained/material passing through remains within a predetermined range of values related to the granulometric curves of the apparatus.

In order to take into account the interval existing between the moment of the transmission of the signal which varies the volume of oil in the actuator and the moment when the device verifies that the adjustment of the crusher has become correct, the range of regulation of the predetermined ratio must be fairly large, or else the signal must be transmitted in the form of pulses with time delay.

One or the other of the weighing apparatuses 5 and 7 may be replaced by a weigher 10 (FIG. 2) which weighs all of the production of the crusher on the conveyor 2. For the automatic remote control of the adjustment of the crusher use is then made either of the ratio material retained/total output or of the ratio material passing through/total output.

As crushing installations almost invariably contain screening and handling devices, the method according to the invention may therefore be carried out in the majority of cases by simply installing weighing machines and a servo control circuit.

The granulometric verification may also be effected on only a fraction of the production of the crusher as shown in FIG. 3, thus restricting the size of the appliances in the control circuit.

In the variant illustrated in FIG. 3, the samplings are effected continuously or at regular intervals at the outlet of the crusher 1 by means of a sampler 10s which diverts the flow of material from the crusher outlet. The materials thus removed are poured into a regulator butter hopper 11, from which they are continuously extracted by a feeder 12 situated above a screening apparatus 3 making a single cut at the selected mesh. Material retained at this mesh is poured on to a conveyor 4 and weighed by an apparatus 5; material passing through is poured on to a conveyor 6 and weighed by a weighing machine 7. As in the example illustrated in FIG. 2, the output signals of the weighing machines are transmitted to the calculator 8, the output of which supplies signals representing the values of the ratio of the weighings; these signals operate the control of the hydraulic device 9 for the purpose of displacing the suspension actuator 10 if necessary.

At the outlet of the sampler 10s the materials which have not been poured into the buffer hopperll fall into a spout 13 and on to a conveyor 14, which carries them to the point of utilization where they rejoin the materials from the conveyor 6.

In order to avoid a hunting action in the above embodiment, it is obviously advantageous to damp the information given by the calculator 8 so that the device 9 will not receive an instruc tion if the variation between the deliveries is too small.

It is also possible to measure on the one hand the total production of the sampling circuit by interposing, between the feeder l2 and the screen 3, a conveyor equipped with a weighing device, and on the other hand the amount of material passing through, or the amount of material passing through, or the amount of material retained on, the mesh of the screen, and to use either the ratio of material passing through/total delivery or the ratio material retained/total delivery for the automatic remote control of the adjustment of the crusher.

After screening and weighing the materials are returned from the sampling circuit to the normal circuit.

The servo control circuit, like that illustrated in FIG. 2, is equipped with means for compensating the time lag existing between the verification and adjustment operations.

Whether the verification is made on the total output or on a fraction of the output, the servo control circuit acts only when the weighing machines register a minimum load, a suitable device (for example a relay) cutting this circuit automatically as soon as the feeding of the conveyors on which the weighings are made is interrupted.

The components of this circuit may be electric, electronic, hydraulic, pneumatic, or of any other nature and components of different natures may be associated with one another to form an automatic servo control assembly.

In the variant illustrated in FIG. 4, the crusher 1 delivers to a conveyor 2, which drops the ground products on to a screen 3, which makes a single cut at the selected mesh for one granulometric class of products. The material passing through drops from the screen 3 on to a conveyor 4 equipped with two weighing machines 5a and 5b, the data produced by which are transmitted to the calculator 8, which transmits signals to the hydraulic device 9.

In this example advantage is taken of the fact that the delivery of a given granulometric class passes through a maximum; use is therefore made of the sign of the derivative of the output function in relation to time and this information is transmitted to the calculator 8 and hydraulic device 9 in order to effect the desired regulating action on the crusher. The weighing machines 5a and 5b give instantaneous outputs which are transmitted simultaneously (that is to say in fact with a time lag 1 dependent on the speed of the band and the distance between the two weighing machines) to the calculator 8, comprising for example a Wheatstone bridge, the imbalance of which is related to the ratio between the deliveries. Any other magnetic, electronic, or other type of device could naturally calculate this ratio.

If the ratio of the weights 5b/ 5a 1 the hydraulic device 9 receives the instruction to increase the tightness of the crusher adjustment i.e. to increase the quantity passing through the screen, and if the ratio 5b/ 5a 1 the device receives instructions to reduce the tightness.

Eventually the deliveries weighed automatically become equal and the adjustment is then such that delivery in the desired granulometric class is a maximum.

FIGS. 5 and 6 illustrate an automatic device for sensing and controlling the position of the grinding parts, which comprises another characteristic of the present invention. The gyratory crusher illustrated in FIG. 5 is provided with an inner grinding cone 17, the position of which varies in relation to that of the outer grinding cone 18, the shaft 19 carrying the inner grinding cone performing both a pendular movement and a rotatory movement due to the forces applied to the grinding cone by the crushing of the materials. In the example, a collar 20 surrounds the shaft 19, on which it is held fixed in respect of rotation by means of flexible parts 27 which absorb the eccentric displacements of the shaft, while enabling the shaft to turn in the collar. A first feeler 21 is secured to the collar 20 and is provided at its other end with a part of circular section, such as a ball or a cylinder 22. A fork 15 constitutes the detector, which is disposed at the level of the ball 22 and follows only the axial displacement of the shaft 19. A second feeler 23,

parallel to the axis of the shaft 19 of the crusher, is connected to the detector 15 and slides freely in a cylinder 24 fixed to the frame 25 of the crusher. Alternatively the feeler 23 may be rigidly connected to a piston slidable in the cylinder 24. The feeler 23 carries a finger 23a which engages in a link of an endless chain 26 passing over three cogged wheels 23' rotatable on shafts fixed in a casing 25a secured to the frame 25 of the crusher. A contactor 16 turns with one of the wheels 23 and effects the recording and control of the movements of the crushing parts.

In the embodiment illustrated, the feeler 23 supporting the detector 15 is prevented from moving by seals 28 in such a manner that the detector is held fixed in order that the movement described by the sphere, cylinder, or roller 22 will be inscribed in the detector without touching its sides.

For the sake of greater simplicity, the operation of the controls and recordings effected with the aid of the detector and of the contactor 16 will be described below at the same time as these controls and recordings themselves.

The contactor 16 connected to the detector is provided with at least one pancake having multiple contact studs, some of which are reserved for the different positions assumed by the movable grinding cone, while the others receive the control orders for the position to be given to said cone.

The contactor 16 is connected to another contactor XXX comprising three pancakes 30, 31, 32 having multiple contact studs, which is controlled by an impulse relay 29 receiving instructions from the weighing measurement transmission apparatus 8, which has the effect either of increasing or of reducing the outlet aperture of the crusher.

Thus, as soon as the shaft 19 has reached the position indicated by this contactor XXX, the shaft position detector connected to the contactor 16 associated with it stops the control cycle, because the desired adjustment has been reached.

In the Example of FIG. 7, the contactor of the hydraulic device 9 contains three pancakes, which fulfill the following functions:

The first (30) is reserved for the raising operations, that is to say it acts through relays 33 and 34 to control the motor-pump unit 36, which injects the fluid into the actuator 35 serving to adjust the relative position of the grinding parts;

The second (31) is reserved for the lowering operations, that is to say it acts through relays 37 and 38 to open the electrically controlled discharge valve 39 of the hydraulic system;

The third (32) serves solely to cancel the raising or lowering operations as soon as the desired position has been reached as indicated by the pancake contactor 16 connected directly to the positioning detector (21-22 in FIG. 5).

The circuit diagram shows how the control operations are carried out by means of the different elements. The contactor XXX, comprising the three pancakes 30, 31, 32 which are mounted coaxially is controlled by an impulse relay 29 capable of acting in either direction. The pancakes are connected electrically in such a manner that there is off setting by one contact stud between the three pancakes, that is to say the stud 1 of the lowering pancake is connected to the stud 2 of the cancelling pancake, which in turn is connected to stud 3 of the raising pancake, etc.

However the contactor 16 is electrically connected to the cancelling pancake 32 without any offsetting of the contact studs and in these circumstances the cancellation of all orders is effected as soon as the detector 21, 22 causes the pancake contactor 16 associated with it to assume the same stud number as that indicated on the cancellation" pancake 32 of the automatic box.

For reasons of safety the electric circuit between all these pancakes and the different control relays is made with low tension current coming from a transformer 49.

Finally, in order to prevent the transmission of abnormal forces to the elements of the crusher, automatic protection means are inserted in the hydraulic and electric circuits.

As soon as an uncrushable body is inserted or jamming occurs between the grinding parts 17, 18 an abnormal force is set up which increases the pressure of the fluid contained in the actuator. The actuator is connected directly to an adjustable maximum manocontact 40 which provides a remote indication of the maximum pressure permissible for each particular crusher. As soon as this pressure is reached, electric contact is made within the pressure gauge and, by means of the relay 41, the electric discharge valve 39 of the hydraulic circuit is opened, which enables the oil to return to the supply tank, thus increasing the outlet opening between the grinding parts.

At the same time a time delay re1ay 42 comes into action, thus preventing the electric pump unit 36 from operating as instructed by the pancake contactor 16 connected to the shaft positioning detector, because the shaft has fallen lower than the preadjusted position, and holds the electrically controlled valve 39 open during the determined time. At the end of this time delay this relay closes the valve 39 by means of a reverser relay 38 and appropriate switches 43 and simultaneously closes the electric circuit for starting up the electric pump 36. Oil is therefore reinjected into the hydraulic actuator 35, the shaft rises again and through the detector drives the pancake contactor 16 connected to it; as soon as the original position has been reached the motor is stopped because the studs of said pancake l6 coincide with those ofthe cancellation pancake 32 in the hydraulic device 9.

ln caseswhere the uncrushable body is of too large dimensions for the maximum outlet aperture of the crusher and where the body therefore has not been discharged, it will once again give rise to excess pressure, whichrepeats the cycle of operations described above. However in order to prevent this cycle from being repeated indefinitely, the time delay relay 42 is provided with an. assembly comprising a step-by step relay 44 which counts the number of cycles in a predetermined time with the aid of another time delay relay 45operated simultaneously from the commencement of the first cycle.

If a predetermined number of cycles is reached before the end of this time delay, an alarm relay circuit 46 is operated and this simultaneously interrupts the current supply tothe crusher motor 47 and also to the electric pump unit 36. If on the other hand the predetermined number of cycles has not been reached during this delay, the time delay relay 45 returns the cycle counter relay 44 to its zero position, that is to say to its original position, and the crusher continues to operate normally.

At the same time, in order to prevent information originating from the weighing measurement assembly through the terminals 48 from acting on the adjustment of the crusher in order to maintain constant granulometry, the step-by-step relay counting the number of cycles cancels this information.

in other words, it is only when the time delay or the zeroising of the step-by-step relay ends that the information coming from the weighing measurement assembly through the terminals 48 can again be received in the contactor XXX in the hydraulic device 9. In the drawing the master switch 50 and the voltage applying contactor relay 51 are also seen.

In Fit]. 8 there is shown diagrammatically a manual control for adjusting the position of the grinding parts. In this control, which acts on an alarm signal, there are seen once again the feeler 21, the part 22, and the detector the detector 15 is rigidly connected to a displaceable cylindrical feeler 223 guided parallel to the axis of the shaft 19 of the crusher on a piston 224 fixed on the frame of the crusher. Here again, the displacement of the cylinder 223 under its own weight is prevented by seals 28 so that the detector 15 is held fixed, normal movement of the part 22 then being inscribed in the detector without touching its sides. The manual control contains in addition a linkage 225 which is provided at one end with a roller 226 disposed on the trajectory of the cylinder 223 and articulated at its other end on a casing 227. This casing can be fixed in various positions by tightening the knob 228', which is adapted to move in a slot in a casing 228 secured to the frame 25. The casing 228 contains a switch 229 operated by a rod 230, one end of which is in contact with the linkage 225 and the switch 229 is connected by wiring 231 to an acoustic alarm 232. When the grinding parts change position, the cylindrical feeler 223 is displaced by the detector and when the bottom end of the feeler 223 reaches the roller 226 of the linkage 225,

the latter drives in the rod" 230 and closes the switch 229, so

that by means of the contactor 233 the signal 232 is operated and at the same time the supply of the grinder motor is interrupted.

We claim:

1. A method of controlling the granulometry of the output material from a grinder comminution apparatus for which a characteristic family of curves has been established defining the granulometry of the material for different settings of the grinding faces comprising:

a. delivering comminuted material from said apparatus to a mesh;

b. making simultaneous measurements of:

total rate of flow of material to the mesh, and rate of flow of material passing the mesh; rate of flow of material retained on the mesh, h

said simultaneous measurements being made at predetermined frequencies; r c. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained. from one of said family of curves; and V d. causing said output signal to generate control forces adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value.

2. A method according to claim 1 wherein the measurements are taken from a stream of comminuted material diverted toa sampling circuit.

3. A method according to claim 1 comprising the step of automa tically sensing the relative positions of the grinding faces of said grinder so as to indicate the setting thereof.

4. A method according to claim 3 including sensing the relative positions of the grinding faces to automatically control the setting thereof.

5. A method of controlling the granulometry of the output material from a grinder comminution apparatus for which a characteristic family of curves has been established defining the granulometry of the material for different settings of the grinder, comprising:

a. delivering comminuted material from said apparatus to a mesh;

b. making simultaneous measurements of the rate of flow of material passing the mesh and the rate of flow of material passing the mesh at a point spaced from the point of the first measurement in the direction of flow, said simultaneous measurements being made at predetermined frequencies;

c. comparing the simultaneous measurements to provide a signal denoting the ratio there-of and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves; and

d. causing said output signal to generated control forces to adjustthe setting of the said grinding faces of said apparatusso as to restore the output signal to the desired value.

6. A method according to claim 5 wherein the output of the apparatus is fed to the mesh.

7. A method according to claim 5 comprising the step of automatically sensing the relative positions of the grinding faces of said apparatus so as to indicate the setting thereof.

8. A method according to claim 7 including sensing the relative positions of the grinding faces to automatically control the setting thereof.

9. A method of controlling the granulometry of the output of material from a gyratory comminution apparatus for which a family of characteristic curves defining the output granulometry for different ratios of feed to the apparatus has been established comprising:

a. delivering comminuted material from said apparatus to a mesh; b. making simultaneous measurements of:

total rate of flow of material to the mesh;

rate of flow of material passing the mesh; said simultaneous measurements being made at predetermined frequencies;

0. comparing the simultaneousmeasurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves; and

causing said output signal to generate control forces to adjust the feed rate so as to restore the output signal to the desired value.

10. In a gyratory comminution apparatus including a device controlling the rate of feed to the apparatus of material to be comminuted, for which apparatus a characteristic family of curves has been established defining the output granulometry of a given material for different rates of feed of material to the apparatus, control equipment comprising:

a. a mesh for receiving comminuted material from .said apparatus;

b. means for simultaneous measurement at said mesh of:

total rate of flow of material to the mesh; rate of flow of material passing the mesh;

c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof; and

d. means for adjusting the spacing of the comminuting faces of said apparatus in response to the output signal.

11. In a comminution apparatus, provided with at least two grinding faces spaced by a distance which is capable of adjustment and for which apparatus a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising:

a. a mesh for receiving comminuted material from said apparatus;

b. means for simultaneous measurement at predetermined frequencies of the rate of flow of material passing the mesh and the rate of flow of material passing the mesh at a point spaced from the point of the first measurement in the direction of flow;

c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof; and

(1. means for adjusting the spacing of the grinding faces in response to the output signal.

12. In a comminution apparatus, provided with at least two grinding faces spaced by a distance which is capable of adjustment, and for which apparatus a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising:

a. a mesh for receiving comminuted material from said apparatus;

b. means for simultaneous measurement at said mesh of:

total rate of flow of material to the mesh, rate of flow of material passing the mesh;

c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof; and

d. means for adjusting the spacing of the grinding faces in response to the output signal.

13. Equipment according to claim 12 wherein the total output of the grinder is fed to the mesh.

14. Equipment according to claim 12 wherein the mesh forms part of a sampling circuit to which part of the output of the grinder is directed.

15. An apparatus according to claim 12 including a conveyor belt and wherein the means for measurement of the rate of flow comprises a weighing machine adapted to weigh the quantity of material on a specific length of conveyor belt.

16. An apparatus according to claim 15 wherein the calculating means comprises an electronic calculator.

17. An apparatus according to claim 16 wherein the grinder is a gyratory grinder.

18. In a gyratory grinder for which a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising:

a. a mesh for receiving ground material from said grinder;

b. means for simultaneous measurement at predetermined frequencies of: total rate of flow of material to the mesh; rate of flow of material passing the mesh;

c. an electronic calculator for comparing said simultaneous measurements to provide a signal denoting the ratio thereof and for comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves;

d. hydraulic apparatus for adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value; and

e. means for sensing and controlling the spacing of the grinding faces.

19. Equipment according to claim 18 wherein the sensing and controlling means comprises a collar surrounding and secured to the shaft so as to allow relative rotary movement of the shaft with respect thereto but so as to prevent relative axial movement therebetween, a feeler rod which is integral with the collar at one end and the other end of which carries a part of circular section, a detector, disposed at the level of said part so as to follow only the axial displacement of the shaft and to allow said part to make all eccentric movements, a second feeler rod rigidly connected to the detector disposed parallel to the axis of the grinder, a cylinder fixed on the frame of the grinder, within which said feeler rod is slidable, and control and recording means connected to said second feeler rod and also to hydraulic means adapted to cause axial displacement of the shaft.

20. Equipment according to claim 19 wherein the collar is prevented from rotating by means of a flexible connection 21. Equipment according to claim 20 wherein the collar, feeler and the part of circular section are replaced by a body of revolution, mounted on the shaft so as to be coaxial and rotatable therewith.

22. Equipment according to claim 20 wherein the detector comprises a fork enclosing the part of circular section the arms of the fork being spaced such that eccentric movements of the part of circular section are inscribed within the space between the arms without touching them.

23. Equipment according to claim 22 wherein the feeler rod is secured to a piston slidable in the cylinder.

24. Equipment according to claim 22 comprising means disposed in the cylinder and preventing movement of the detector under its own weight.

25. Equipment according to claim 24 wherein the means disposed in the cylinder comprise friction seals disposed between the feeler rod and the cylinder.

26. In a gyratory grinder for which a characteristic family of curves has been established defining the granulometry of a given material for different spacing of the grinding faces control equipment comprising:

a. a mesh for receiving ground material from said grinder;

b. means for simultaneous measurement of:

total rate of flow of material to the mesh, and

rate of flow of material passing the mesh; said simultaneous measurements being made at predetermined frequencies,

c. an electronic calculator for comparing said simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves,

d. hydraulic apparatus for adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value, and

e. means for sensing and controlling the spacing of the grinding faces, comprising a collar surrounding and secured to the shaft so as to allow relative rotary move ment of the shaft with respect thereto but so as to prevent relative axial movement therebetween, a feeler rod which is integral with the collar at one end and the other end of which carries a part of circular section, a detector disposed at the level of said part so as to follow only the axial displacement of the shaft and to allow said part to make all eccentric movements, a second feeler rod rigidly connected to the detector and parallel to the axis of the crusher in such a manner as to be able to slide freely in a cylinder fixed on the frame of the crusher, said second feeler rod being connected to control and recording means in electrical contact with hydraulic means adapted to cause axial displacement of the shaft, said control and recording means comprising at least one rotatable con tactor mechanically connected to the detector in such a manner so as to convert axial movement of the latter into rotational movement of the former, the contactor comprising a multicontact pancake switch. in which a number of contacts serve to indicate the relative positions of the grinding faces and other contacts serve to allow the transmission of signals to thehydraulicdevice to adjust the relative positions of the grinding faces.

27. Equipment according to claim 26 including an overload device adapted to separate the grinding faces of the crusher upon fluid pressure in the actuator exceeding a predetermined value. Y

28. Equipment according to claim 27 wherein the overload device includes time delay means to prevent immediate correction of the relative position of the grinding faces upon the operation of the overload device.

29. Equipment according to claim 28 including means for cancelling the output signal from the calculating means during operation of the overload device.

30. Equipment according to claim 29 wherein further time delay means are provided whereby the crusher can be stopped if the overload device operates more than a predetermined number of times during the activation period of the further time delay.

31. A method of controlling the granulometry of the output material from a grinder comminution apparatus for which a characteristic family of curves has been established defining the granulometry of the material for different settings of the grinding faces comprising: 7

a. delivering comminuted material from said apparatus to a mesh;

b. making simultaneous measurements of total rate of flow of material to the mesh, and rate of flow of material retained on the mesh, said simultaneous measurements being made at predetermined frequencies;

c. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves; and causingsaid output signal to generate control forces adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value.

32. A method of controlling the granulometry of the output material from a grinder comminution apparatus for which a characteristic family of curves has been established defining the granulometry of the material for different settings of the grinding faces comprising:

a. delivering comminuted material from said apparatus to a mesh;

b. making simultaneous measurements of rate of flow of material passing the mesh, and rate of flow of material retained on the mesh,simultaneous measurements being made at predetermined frequencies;

c. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value' to provide an output signal, said desired value being obtained from one of said family of curves, and p d. causing said output signal to generated control forces adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value.

33. A method of controlling the granulometry of the output of material from a gyratory comminution apparatus for which a family of characteristic curves defining the output granulometry for different ratios of feed to theapparatus has been established comprising:

a. delivering comminuted material from said apparatus to a mesh,

b. making simultaneous measurements of total rate of flow of material to the mesh, and rate of flow of material retained on the mesh, said' simultaneous measurements being made at predetermined frequencies;

c. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide anoutput signal, said desired value being obtained from one of said family of curves, and

d. causing said output signalto' generate control forces to adjust the feed rate so as to restore the output signal to the desired value.

34. A method of controlling the granulometry of the output of material from a gyratory comminution apparatus for which a family of characteristic curves defining the output granulometry for different ratios of feed to the apparatus has been established comprising:

a. delivering comminuted material from said apparatus to a mesh;

b. making simultaneous measurements of rate of flow of material passing the mesh, and rate of flow of material retained on the mesh, said simultaneous measurements being made at predetermined frequencies;

c. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves, and

d. causing said output signal to generate control forces to adjust the feed rate so as to restore the output signal to the desired value.

35. In a gyratory comminution apparatus including a device controlling the rate of feed to the apparatus of material to be comminuted, for which apparatus a characteristic family of curves has been established defining the output granulometry of a given material for different rates of feed of material to the apparatus, control equipment comprising:

a. a mesh for receivingcomminuted material from said apparatus; Y

b. means for simultaneous measurement at said mesh of total rate of flow of material to the mesh, and rate of flow of material retained on the mesh;

c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof; and

d. means for adjusting the spacing of the comminuting faces of said apparatus in response to the output signal.

36. In a gyratory comminution apparatus including a device controlling the rate of feed to theapparatus of material to be comminuted, for which apparatus a characteristic family of curves has been established defining the output granulometry of a given material for different rates of feed of material to the apparatus, control equipment comprising;

a. a mesh for receiving comminuted material from said apparatus; i

b. means for simultaneou's nieasurement at said mesh of rate of flow of material passing the mesh, and rate of flow of material retained on the mesh;

c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof, and

d. means for adjusting the spacing of the comminuting faces of said apparatus in response to the output signal.

37. In a comminution apparatus, provided with at least two grinding faces spaced by a distance which is capable of adjustment, and for which apparatus a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising;

a. a mesh for receiving comminuted material from said ap paratus;

b. means for simultaneous measurement at said mesh of total rate of flow of material to the mesh, and rate of flow of material retained on the mesh;

0. calculating means for comparing the values of the two measurements and for providing an output signal propor tional to the ratio thereof and d. means for adjusting the spacing of the grinding faces in response to the output signal.

38. In a comminution apparatus, provided with at least two grinding faces spaced by a distance which is capable of adjustment, and for which apparatus a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising;

a. a mesh for receiving comminuted material from said apparatus;

b. means for simultaneous measurement at said mesh of rate of flow of material passing the mesh, and rate of flow of material retained on the mesh;

c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof and d. means for adjusting the spacing of the grinding faces in response to the output signal.

39. In a gyratory grinder for which a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising:

a. a mesh for receiving ground material from said grinder;

b. means for simultaneous measurement at predetermined frequencies of total rate of flow of material to the mesh, and rate of flow of material retained on the mesh;

0. an electronic calculator for comparing said simultaneous measurements to provide a signal denoting the ratio thereof and for comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves;

d. hydraulic apparatus for adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value, and

e. means for sensing and controlling the spacing of the grinding faces.

40. In a gyratory grinder for which a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising;

a. a mesh for receiving round material from said grinder,

b. means for simultaneous measurement at predetermined frequencies of: rate of flow of material passing the mesh, and rate of flow of material retained on the mesh,

0. an electronic calculator for comparing said simultaneous measurements to provide a signal denoting the ratio thereof and for comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves;

d. hydraulic apparatus for adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value, and e. means for sensing and controlling the spacing of the grinding faces. 

2. A method according to claim 1 wherein the measurements are taken from a stream of comminuted material diverted to a sampling circuit.
 3. A method according to claim 1 comprising the step of automatically sensing the relative positions of the grinding faces of said grinder so as to indicate the setting thereof.
 4. A method according to claim 3 including sensing the relative positions of the grinding faces to automatically control the setting thereof.
 5. A method of controlling the granulometry of the output material from a grinder comminution apparatus for which a characteristic family of curves has been established defining the granulometry of the material for different settings of the grinder, comprising: a. delivering comminuted material from said apparatus to a mesh; b. making simultaneous measurements of the rate of flow of material passing the mesh and the rate of flow of material passing the mesh at a point spaced from the point of the first measurement in the direction of flow, said simultaneous measurements being made at predetermined frequencies; c. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves; and d. causing said output signal to generated control forces to adjust the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value.
 6. A method according to claim 5 wherein the output of the apparatus is fed to the mesh.
 7. A method according to claim 5 comprising the step of automatically sensing the relative positions of the grinding faces of said apparatus so as to indicate the setting thereof.
 8. A method according to claim 7 including sensing the relative positions of the grinding faces to automatically control the setting thereof.
 9. A method of controlling the granulometry of the output of material from a gyratory comminution apparatus for which a family of characteristic curves defining the output granulometry for different ratios of feed to the apparatus has been established comprising: a. delivering comminuted material from said apparatus to a mesh; b. making simultaneous measurements of: total rate of flow of material to the mesh; rate of flow of material passing the mesh; said simultaneous measurements being made at predetermined frequencies; c. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves; and d. causing said output signal to generate control forces to adjust the feed rate so as to restore the output signal to the desired value.
 10. In a gyratory comminution apparatus including a device controlling the rate of feed to the apparatus of material to be comminuted, for which apparatus a characteristic family of curves has been established defining the output granulometry of a given material for different rates of feed of material to the apparatus, control equipment comprising: a. a mesh for receiving comminUted material from said apparatus; b. means for simultaneous measurement at said mesh of: total rate of flow of material to the mesh; rate of flow of material passing the mesh; c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof; and d. means for adjusting the spacing of the comminuting faces of said apparatus in response to the output signal.
 11. In a comminution apparatus, provided with at least two grinding faces spaced by a distance which is capable of adjustment and for which apparatus a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising: a. a mesh for receiving comminuted material from said apparatus; b. means for simultaneous measurement at predetermined frequencies of the rate of flow of material passing the mesh and the rate of flow of material passing the mesh at a point spaced from the point of the first measurement in the direction of flow; c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof; and d. means for adjusting the spacing of the grinding faces in response to the output signal.
 12. In a comminution apparatus, provided with at least two grinding faces spaced by a distance which is capable of adjustment, and for which apparatus a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising: a. a mesh for receiving comminuted material from said apparatus; b. means for simultaneous measurement at said mesh of: total rate of flow of material to the mesh, rate of flow of material passing the mesh; c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof; and d. means for adjusting the spacing of the grinding faces in response to the output signal.
 13. Equipment according to claim 12 wherein the total output of the grinder is fed to the mesh.
 14. Equipment according to claim 12 wherein the mesh forms part of a sampling circuit to which part of the output of the grinder is directed.
 15. An apparatus according to claim 12 including a conveyor belt and wherein the means for measurement of the rate of flow comprises a weighing machine adapted to weigh the quantity of material on a specific length of conveyor belt.
 16. An apparatus according to claim 15 wherein the calculating means comprises an electronic calculator.
 17. An apparatus according to claim 16 wherein the grinder is a gyratory grinder.
 18. In a gyratory grinder for which a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising: a. a mesh for receiving ground material from said grinder; b. means for simultaneous measurement at predetermined frequencies of: total rate of flow of material to the mesh; rate of flow of material passing the mesh; c. an electronic calculator for comparing said simultaneous measurements to provide a signal denoting the ratio thereof and for comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves; d. hydraulic apparatus for adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value; and e. means for sensing and controlling the spacing of the grinding faces.
 19. Equipment according to claim 18 wherein the sensing and controlling means comprises a collar surrounding and secured to the shaft so as to allow relative rotary movement of the shaft with respect thereto but so as to prevent relatIve axial movement therebetween, a feeler rod which is integral with the collar at one end and the other end of which carries a part of circular section, a detector, disposed at the level of said part so as to follow only the axial displacement of the shaft and to allow said part to make all eccentric movements, a second feeler rod rigidly connected to the detector disposed parallel to the axis of the grinder, a cylinder fixed on the frame of the grinder, within which said feeler rod is slidable, and control and recording means connected to said second feeler rod and also to hydraulic means adapted to cause axial displacement of the shaft.
 20. Equipment according to claim 19 wherein the collar is prevented from rotating by means of a flexible connection
 21. Equipment according to claim 20 wherein the collar, feeler and the part of circular section are replaced by a body of revolution, mounted on the shaft so as to be coaxial and rotatable therewith.
 22. Equipment according to claim 20 wherein the detector comprises a fork enclosing the part of circular section the arms of the fork being spaced such that eccentric movements of the part of circular section are inscribed within the space between the arms without touching them.
 23. Equipment according to claim 22 wherein the feeler rod is secured to a piston slidable in the cylinder.
 24. Equipment according to claim 22 comprising means disposed in the cylinder and preventing movement of the detector under its own weight.
 25. Equipment according to claim 24 wherein the means disposed in the cylinder comprise friction seals disposed between the feeler rod and the cylinder.
 26. In a gyratory grinder for which a characteristic family of curves has been established defining the granulometry of a given material for different spacing of the grinding faces control equipment comprising: a. a mesh for receiving ground material from said grinder; b. means for simultaneous measurement of: total rate of flow of material to the mesh, and rate of flow of material passing the mesh; said simultaneous measurements being made at predetermined frequencies, c. an electronic calculator for comparing said simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves, d. hydraulic apparatus for adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value, and e. means for sensing and controlling the spacing of the grinding faces, comprising a collar surrounding and secured to the shaft so as to allow relative rotary movement of the shaft with respect thereto but so as to prevent relative axial movement therebetween, a feeler rod which is integral with the collar at one end and the other end of which carries a part of circular section, a detector disposed at the level of said part so as to follow only the axial displacement of the shaft and to allow said part to make all eccentric movements, a second feeler rod rigidly connected to the detector and parallel to the axis of the crusher in such a manner as to be able to slide freely in a cylinder fixed on the frame of the crusher, said second feeler rod being connected to control and recording means in electrical contact with hydraulic means adapted to cause axial displacement of the shaft, said control and recording means comprising at least one rotatable contactor mechanically connected to the detector in such a manner so as to convert axial movement of the latter into rotational movement of the former, the contactor comprising a multicontact ''pancake'' switch in which a number of contacts serve to indicate the relative positions of the grinding faces and other contacts serve to allow the transmission of signals to the hydraulic device to adjust the relative positions of the grinding faces.
 27. Equipment according to claiM 26 including an overload device adapted to separate the grinding faces of the crusher upon fluid pressure in the actuator exceeding a predetermined value.
 28. Equipment according to claim 27 wherein the overload device includes time delay means to prevent immediate correction of the relative position of the grinding faces upon the operation of the overload device.
 29. Equipment according to claim 28 including means for cancelling the output signal from the calculating means during operation of the overload device.
 30. Equipment according to claim 29 wherein further time delay means are provided whereby the crusher can be stopped if the overload device operates more than a predetermined number of times during the activation period of the further time delay.
 31. A method of controlling the granulometry of the output material from a grinder comminution apparatus for which a characteristic family of curves has been established defining the granulometry of the material for different settings of the grinding faces comprising: a. delivering comminuted material from said apparatus to a mesh; b. making simultaneous measurements of total rate of flow of material to the mesh, and rate of flow of material retained on the mesh, said simultaneous measurements being made at predetermined frequencies; c. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves; and d. causing said output signal to generate control forces adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value.
 32. A method of controlling the granulometry of the output material from a grinder comminution apparatus for which a characteristic family of curves has been established defining the granulometry of the material for different settings of the grinding faces comprising: a. delivering comminuted material from said apparatus to a mesh; b. making simultaneous measurements of rate of flow of material passing the mesh, and rate of flow of material retained on the mesh, said simultaneous measurements being made at predetermined frequencies; c. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves, and d. causing said output signal to generated control forces adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value.
 33. A method of controlling the granulometry of the output of material from a gyratory comminution apparatus for which a family of characteristic curves defining the output granulometry for different ratios of feed to the apparatus has been established comprising: a. delivering comminuted material from said apparatus to a mesh, b. making simultaneous measurements of total rate of flow of material to the mesh, and rate of flow of material retained on the mesh, said simultaneous measurements being made at predetermined frequencies; c. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves, and d. causing said output signal to generate control forces to adjust the feed rate so as to restore the output signal to the desired value.
 34. A method of controlling the granulometry of the output of material from a gyratory comminution apparatus for which a family of characteristic curves defining the output granulometry for different ratios of feed to the apparatus has been established comprising: a. delivering comminuted material from said apparatus to a mesh; b. making simultaneOus measurements of rate of flow of material passing the mesh, and rate of flow of material retained on the mesh, said simultaneous measurements being made at predetermined frequencies; c. comparing the simultaneous measurements to provide a signal denoting the ratio thereof and comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves, and d. causing said output signal to generate control forces to adjust the feed rate so as to restore the output signal to the desired value.
 35. In a gyratory comminution apparatus including a device controlling the rate of feed to the apparatus of material to be comminuted, for which apparatus a characteristic family of curves has been established defining the output granulometry of a given material for different rates of feed of material to the apparatus, control equipment comprising: a. a mesh for receiving comminuted material from said apparatus; b. means for simultaneous measurement at said mesh of total rate of flow of material to the mesh, and rate of flow of material retained on the mesh; c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof; and d. means for adjusting the spacing of the comminuting faces of said apparatus in response to the output signal.
 36. In a gyratory comminution apparatus including a device controlling the rate of feed to the apparatus of material to be comminuted, for which apparatus a characteristic family of curves has been established defining the output granulometry of a given material for different rates of feed of material to the apparatus, control equipment comprising; a. a mesh for receiving comminuted material from said apparatus; b. means for simultaneous measurement at said mesh of rate of flow of material passing the mesh, and rate of flow of material retained on the mesh; c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof, and d. means for adjusting the spacing of the comminuting faces of said apparatus in response to the output signal.
 37. In a comminution apparatus, provided with at least two grinding faces spaced by a distance which is capable of adjustment, and for which apparatus a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising; a. a mesh for receiving comminuted material from said apparatus; b. means for simultaneous measurement at said mesh of total rate of flow of material to the mesh, and rate of flow of material retained on the mesh; c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof and d. means for adjusting the spacing of the grinding faces in response to the output signal.
 38. In a comminution apparatus, provided with at least two grinding faces spaced by a distance which is capable of adjustment, and for which apparatus a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising; a. a mesh for receiving comminuted material from said apparatus; b. means for simultaneous measurement at said mesh of rate of flow of material passing the mesh, and rate of flow of material retained on the mesh; c. calculating means for comparing the values of the two measurements and for providing an output signal proportional to the ratio thereof and d. means for adjusting the spacing of the grinding faces in response to the output signal.
 39. In a gyratory grinder for which a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising: a. a mesh for receiving ground material from said grinder; b. means for simultaneous measurement at predetermined frequencies of total rate of flow of material to the mesh, and rate of flow of material retained on the mesh; c. an electronic calculator for comparing said simultaneous measurements to provide a signal denoting the ratio thereof and for comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves; d. hydraulic apparatus for adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value, and e. means for sensing and controlling the spacing of the grinding faces.
 40. In a gyratory grinder for which a characteristic family of curves has been established defining the granulometry of a given material for different spacings of the grinding faces, control equipment comprising; a. a mesh for receiving round material from said grinder, b. means for simultaneous measurement at predetermined frequencies of: rate of flow of material passing the mesh, and rate of flow of material retained on the mesh, c. an electronic calculator for comparing said simultaneous measurements to provide a signal denoting the ratio thereof and for comparing this signal with a desired value to provide an output signal, said desired value being obtained from one of said family of curves; d. hydraulic apparatus for adjusting the setting of the said grinding faces of said apparatus so as to restore the output signal to the desired value, and e. means for sensing and controlling the spacing of the grinding faces. 